The present invention relates to power supplies for use with gas discharge lamps. More particularly, the present invention relates to a power supply for maintaining a constant brightness in a gas discharge lamp even in the presence of variations in input voltage to the power supply.
In general, conventional power supplies for a gas discharge lamp or tube limit the current provided to the lamp because the load corresponding to the lamp has a very low-slope impedance, which may be negative for certain values of input current, and which may lead to an unstable operating point for the tube.
Conventional power supplies for gas discharge lamps often do not compensate for variations in input voltage to the power supplies. Such variations in input voltage cause variations in the output current to the lamps, which result in variations in the brightness in the lamps as a function of the input voltage variations.
In many applications in which gas discharge lamps are used, it is desirable to have a reasonably constant brightness in the lamps even when fluctuations in input voltage occur. For example, in an application in which several power supplies are used together to power a lighting display formed of several lamps, with each power supply driving a separate lamp of the lighting display, the aesthetic value of the lighting display increases if the brightness or light intensity in each of the lamps is close in value. The lamps are usually connected by a parallel bus in a so-called "daisy chain" manner, such that the input voltage to a particular tube of the lighting display depends on the lamp's position on the bus. If the output current from each of the power supplies is not maintained at a reasonably constant value due to variations in the input voltage, then the brightness in each of the lamps in the lighting display will vary depending on its position on the bus.